Piezoelectric resonator devices such as crystal resonators, crystal filters, and crystal oscillators are examples of electronic components that require hermetic enclosure. In each component, a metal film electrode is formed on a surface of a crystal resonator plate, and the crystal resonator plate (specifically, the metal film electrode) is hermetically enclosed so as to protect the metal film electrode from ambient air.
These piezoelectric resonator devices increasingly employ hermetic housing of piezoelectric oscillation plates (crystal resonator plates) in packages made of insulating material such as ceramic in view of demands associated with surface mounting of parts. For example, patent citation PLT 1 discloses a package that includes: a base (mounting board) made of a ceramic material with a mounting portion for a crystal resonator plate; and a lid (cover) having an inverted U-shaped cross-section. The package hermetically encloses the crystal resonator plate, and is mounted on a circuit substrate and bonded with a conductive bonding material such as solder.
The conventional piezoelectric resonator device includes a terminal electrode on a bottom face of the base. The terminal electrode is extended from the bottom face to a side surface of the base through a castellation on the side surface of the base, so as to ensure confirmation of a connection state associated with the capillary action of solder (conductive bonding material).
The conventional piezoelectric resonator device is generally mounted on a circuit substrate that is what is called a glass epoxy substrate made of a glass fiber mesh impregnated with an epoxy resin material, for facilitating the fabrication and saving the cost. Also, a solder paste is applied on an electrode pattern of the circuit substrate by screen printing or the like. Then the piezoelectric resonator device package is mounted on the circuit substrate with the terminal electrode of the piezoelectric resonator device package being overlaid on the electrode pattern of the circuit substrate. Thereafter, the solder paste is melted in a melting furnace (a heating furnace, etc.) in order to bond the piezoelectric resonator device to the circuit substrate with the solder.